One method for increasing the density of microelectronic circuits for electronic devices (such as computers, portable phones, etc.) is to stack two or more microelectronic dies on top of each other. Accordingly, this arrangement can provide additional circuits within the same footprint normally occupied by a single die. FIG. 1 is a partially schematic, cross-sectional elevational view of an existing stacked die package 10. The package 10 includes a substrate 40 that carries a first die 20 and a stacked second die 30. The first die 20 is attached to the substrate 40 with a paste layer 14. A spacer 12 is attached to the first die 20 with a first tape layer 13a. The second die 30 is attached to the spacer 12 with a second tape layer 13b. 
The first die 20 includes first die bond pads 21 that are coupled to corresponding first substrate bond pads 41a with first wirebonds 50a. The first substrate bond pads 41a are coupled to external substrate bond pads 41c with vias. The external substrate bond pads 41c each have a substrate solder ball 42 to provide communication between the first die 20 and devices located external to the package 10. Similarly, the second die 30 includes second die bond pads 31 coupled to corresponding second substrate bond pads 41b with second wirebonds 50b. The second substrate bond pads 41b are coupled to additional external substrate bond pads 41c to provide communication between the second die 30 and devices external to the package. Once the first and second wirebonds 50a, 50b are connected, the substrate 40, the first die 20, and the second die 30 can be at least partially enclosed with an encapsulant 12 to protect these components.
One feature of an arrangement shown in FIG. 1 is that the overall thickness of the package 10 can be significantly greater than the combined thicknesses of the substrate 40, the first die 20, and the second die 30. As a result, the package 10 can be difficult to integrate into devices having very tight vertical clearances. Accordingly, the benefits of the stacked die arrangement provided to the standard size devices in which they are incorporated may not be available for very compact devices.